Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.74	7.701%	$40.6464	$40.65	$40.65	$40.60
Purchase #2	$42.55	7.662%	$45.8102	$45.81	$45.80	$45.80
Purchase #3	$139.91	4.611%	$146.3613	$146.36	$146.35	$146.40
Purchase #4	$66.77	7.705%	$71.9146	$71.91	$71.90	$71.90
Purchase #5	$115.30	4.643%	$120.6534	$120.65	$120.65	$120.70
Purchase #6	$45.34	4.872%	$47.549	$47.55	$47.55	$47.50
Purchase #7	$19.42	3.821%	$20.162	$20.16	$20.15	$20.20
7 purchase totals =	$467.03		$493.0969	$493.09	$493.05	$493.10